On one hand, 3GPP LTE (Long Term Evolution) is the name given to a project within the Third Generation Partnership Project (3GPP) to improve the UMTS mobile phone standard to cope with future requirements. Goals have included so far improving efficiency, lowering costs, improving services, making use of new spectrum opportunities, and better integration with open standards. In another hand, International Mobile Telecommunication (IMT)-Advanced has aimed at providing enhanced peak data rates to support advanced services and applications (100 Mbit/s for high and 1 Gbit/s for low mobility were established as targets for research). Altogether, future 3GPP LTE-Advanced systems will require wider system bandwidth, e.g. up to 100 MHz, to achieve such high target peak data rates. However, it may become a challenge to find contiguous spectrum allocations that can accommodate such wide bandwidth, since the spectrum bands are limited. Furthermore, spectrum segments used by operators but not necessarily located contiguously or in the same frequency band may be considered. At the same time, backward compatibility towards LTE Release-8 (prior to LTE-Advanced) should be ensured. Carrier aggregation (CA) is a natural choice that could either meet the bandwidth extension requirement or ensure sufficient backward compatibility towards LTE Release-8. In Carrier Aggregation, multiple Component Carriers (CCs) are aggregated according to the desired LTE-Advanced system bandwidth. These CCs are either LTE Release-8 compatible or designed specially to support new LTE Advanced features. A LTE Release-8 user equipment may receive one of these component carriers, while an LTE-Advanced user equipment may simultaneously access multiple component carriers. Compared to other approaches, carrier aggregation does not require extensive changes of LTE physical layer structure, and can reuse the most of the existing implementations.
When Carrier Aggregation is implemented, existing Hybrid Automatic Repeat Request method is an important aspect. The Hybrid Automatic Repeat Request (Hybrid ARQ, H-ARQ) is a variation of an Automatic Repeat Request (ARQ) error control method, which performs better ARQ, particularly over wireless channels. An example of HARQ, also referred to as Type I HARQ, combines Forward Error Correction (FER) and ARQ by encoding a data block and error-detection information (such as Cyclic Redundancy Check (CRC)) with an error-correction code (such as e.g. Reed-Solomon code or Turbo code) prior to transmission. When the coded data block is received, the receiver first decodes the error-correction code. If the channel quality is good enough, all transmission errors should be correctable, and the receiver may derive the correct data block. If the channel quality is not good enough and not all transmission errors can be corrected, the receiver detects this situation using the error-detection code, then the received coded data block may be discarded or stored and a retransmission is requested by the receiver, similar to ARQ. In practice, incorrectly received coded data blocks (i.e. erroneous data blocks) are often stored at the receiver rather than discarded, and when the retransmitted block is received, the two blocks are combined (chase combining) before being fed to the decoder of the error-correction code. This can increase the probability of successful decoding. An another existing solution is Type II/III HARQ, or incremental redundancy HARQ, where different (re)transmissions are coded differently rather than repeating the same coded bits as in chase combining. Performance is improved, since coding is effectively done across retransmissions. The difference between type III HARQ and type II HARQ is that the retransmission packets in Type III HARQ can be decoded by themselves. The HARQ method uses at least one HARQ process and some HARQ process entities, here under referred to, respectively, as set of transmission control frames and transmission control frames. Each transmission control frame may comprise one or more header and one or more data blocks. Each transmission control frames are transmitted between an emitter and a receiver in a telecommunication network. In other words, data blocks are transmitted using transmission control frames. Moreover, the plurality of carriers may be divided into time intervals or time slots, wherein each transmission control frame is transmitted on each carrier at each time interval (as described here under in reference to FIG. 3).
In wireless Carrier Aggregation (CA) systems, for example, one User Equipment (UE) may be scheduled simultaneously on multiple (i.e. a plurality of) Component Carriers (CCs). Therefore, re-transmission of data blocks may be allowed across CCs in order to better exploit frequency diversity. In other words, errors detected in a data block transmitted in a first carrier are less likely to happen in retransmission of the same data block on another carrier at a different frequency. HARQ process entities may be grouped into sets, each set being dedicated, for example, to a given user equipment or data stream. Multiple stop-and-wait HARQ process entities may be transmitted in parallel on the same or different CC(s) so that while one HARQ process is waiting for an acknowledgement for a given HARQ process entity other HARQ process entities may use the carrier(s) to send additional packets. For each user equipment, there may be one HARQ process or transmission control frame process, each comprising a plurality of HARQ process entities or transmission control frames. The number of HARQ process entities should be in accordance with the roundtrip time between the emitter and the receiver to allow for continuous transmission, including the respective processing time of the data blocks, HARQ process entities and HARQ process. For example, the emitter and the receiver may be a user equipment (UE) and a eNodeB (station or radio controller element of the 3GPP LTE network) or vice-and-versa. Using a larger number of HARQ process entities than required by the roundtrip time does not provide any gain, but rather introduces unnecessary delays between retransmissions. Since processing time of the of the data blocks, HARQ process entities and HARQ process for an eNodeB may differ among different implementations, the number of HARQ process entities may be configurable. For example, a set of eight HARQ process entities or transmission control frames may be used for a given component carrier or user equipment or data stream. When Carrier Aggregation is used, one HARQ process (i.e. a set of HARQ process entities) may be used per component carrier (called here under “carrier” for simplification purposes) to increase the number of HARQ process entities (and therefore the bandwidth) for one user equipment.
To perform operations such as soft combining (cohesion of data streams from multiple base stations or eNodeB that share a common time line and are operated according to it), in-sequence delivery and so on, the UE has to identify the HARQ process entities or transmission control frames of the carrier(s) it transmits on.
HARQ process sets may be flexibly mapped to carriers up-link and down-link. It allows retransmission across carriers, which may derive higher frequency diversity gain or flexible scheduling gain. However, additional bits are needed in the header (here under called transmission control frame indication) of each transmission control frame are needed to identify the previous carrier the transmission control frame was transmitted onto. This seems to be a large signalling overhead, especially when using many carriers. This indication may be used for instance by an emitter to inform a receiver of which HARQ process set has been used in a control channel (such as e.g. a Physical Downlink Shared Channel (PDSCH) or a Physical Uplink Shared Channel (PUSCH)). It may also be considered that flexible HARQ process sets mapping to carriers is allowed to a limited range only (e.g. only for retransmissions within carrier pairs, etc. . . . ) for signalling efficiency.
As described in document “3GPP TSG RAN WG1 #56, R1-090652, “HARQ mapping across aggregated component carriers”, LG Electronics, 9-13 Feb., 2009” which is considered as the most relevant state of the art document: the simplest way is to list all of the possibilities and inform the destination, requiring thus n.[log2 n] bits of signalling. The major drawback with this method is that there is a need for much control signalling and, in particular, control signalling overheads are too big.
Today there is no solution to efficiently reduce signalling overhead that allow reducing signalling and thus improving efficiency of such wireless telecommunication systems.
Today there is a need for a control signalling solution that can be easily implemented on the existing communication infrastructures.